The technical field of this disclosure is disc brakes for vehicles and in particular a brake rotor that deforms symmetrically when expanding radially due to elevated heat conditions.
Non-uniform pressure distribution of the brake pads applied to the rotor is a key contributor to certain types of brake squeal. Non-uniform pressure distribution can result when linings wear unevenly or become tapered. The taper pattern can take the form of lead-to-trail or inside (hub) to outside diameter. Nonuniform pressure distribution due to tapered wear can result from caliper and shoe deflections or by rotor deformation due to thermal expansion.
Rotor deformation can occur due to thermal expansion of the rotor at high temperatures. During operation, heat is generated in the brake rotor as the kinetic energy of the moving vehicle is converted to heat energy through the frictional interface between brake pads forcibly applied against the brake rotor friction plates. One effect of overheating of brake components is warping or coning of the brake rotor. It is believed that as the rotor expands in the radial direction, the hat section that is bolted to the hub acts as a restraint to prevent the outboard surface plate (cheek) from expanding. The inboard plate attached to the outboard plate by way of the vanes is free at the inside diameter. Therefore, the inboard plate has less resistance to radial expansion than the outboard plate. Consequently, as the rotor expands in the radial direction due to elevated temperature conditions, a lateral deformation or a coned shape results. This coning of the rotor at elevated temperatures can cause a tapered wear condition from the inside diameter to the outside diameter. The inboard lining will show more wear at the inside diameter and the outboard lining shows more wear at the outside diameter. When the rotor cools back towards the original temperature, the pad pressure distribution becomes different than a rotor in an unworn condition. The result is higher pad pressures at the outside diameter of the inboard pad and at the inside diameter of the outboard pad. This non-uniform pressure distribution can contribute to the excitation of certain squeal modes, especially at lower temperatures and low pressures.
As shown in FIGS. 1 and 2A, a conventional rotor 10 includes hat section or central attachment portion 12 of a rotor attached to an associated axle (not shown). The hat section 12 is attached to a friction portion 14. The friction portion 14 includes a pair of spaced, parallel rotor plates 16, 18 (also referred to as a friction plate or cheek). The friction portion 14 is attached to the central attachment portion 12 by an extending, attachment or side portion 20 that attaches the hat portion 10 of the rotor 12 directly to the outboard rotor plate 16. It is believed that this conventional method of attachment contributes to the non-symmetrical expansion of the friction plates.
FIG. 1 illustrates a conventional rotor 10 with an outboard plate 16 attached to an inboard plate 18 by a solid connecting portion represented at 30. It can be seen that the rotor plates 16, 18 (held in a parallel relationship by the connecting portion 30) are held in a parallel orientation with the central attachment portion 12. Since the central attachment portion 12 is perpendicular to an associated axle (not shown) oriented in direction A, the friction portion 14 is also held perpendicular to the axle.
FIG. 2A illustrates the conventional rotor 10 with an extending side portion 20. The extending side portion 20 extends at right angles from the central attachment portion 12. Friction portion 14 has plates 16, 18 oriented at right angles to the extending side portion 20. As shown represented in FIG. 2B and illustrated in FIGS. 3 and 4, when heated to an elevated temperature, the friction plates 16, 18 are deformed out of alignment with the axial direction Y.
Therefore, it would be advantageous to provide a brake rotor having thermally symmetric expansion properties to reduce rotor distortion during an elevated temperature condition.
One aspect of the present invention provides a brake rotor including a central disc portion and an extending portion located at a periphery of the central disc portion. A friction portion having a first friction plate is attached to the extending portion and a second friction plate is attached to the first friction plate. The extending portion is adapted to allow the first friction plate to expand in a radial direction in an amount substantially equal to the second friction plate under a condition of elevated temperature.
In another aspect of the present invention, the first friction plate, under a condition of elevated temperature, expands a first radial distance and the second friction plate expands a second radial distance. The first radial distance is substantially equal to the second radial distance.
In another aspect of the present invention, the first friction plate is an outboard friction plate and the second friction plate is an inboard friction plate. In yet another embodiment, the first friction plate is an inboard friction plate and the second friction plate is an outboard friction plate.
In another aspect of the present invention, the extending portion of the brake rotor can include one or more of a U-shape, an arcuate shape, a V-shape, and a double opposed spring shape.
Another aspect of the present invention includes a method for allowing substantially equal radial expansion of an inboard and an outboard friction plate in a brake rotor under elevated temperatures. The method includes providing an extending portion between a central attachment portion of a brake rotor and the outboard friction plate and expanding the extending portion in the radial direction a distance to maintain substantially equal radial movement of the outboard friction plate and inboard friction plate.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defamed by the appended claims and equivalents thereof.